Hydraulic pressure operated switch



y 29, 1955 J. D. BUCHANAN HYDRAULIC PRESSURE OPERATED SWITCH Filed Feb. 16, 1953 J. 0; BUCHANAN,

IN VEN TOR.

A 7'7'ORNEY.

Unite States atent HYDRAULIC PRESSURE OPERATED SWITCH J. D. Buchanan, Burbank, Calif.

Application February 16, 1953, Serial No. 337 ,044

7 Claims. (Cl. 20083) The invention relates to a hydraulic pressure operated switch, and more particularly to a switch controlling a signal to show when the fluid pressure reaches a certain low value.

The various parts of an aeroplane are operated by hydraulic motors or pistons supplied with hydraulic oil under pressure. Such devices will not operate properly if the pressure reaches a certain low value, and it has been proposed to provide a signal light at the pilots position in order to show the condition of such fluid pressure. The design of a suitable switching mechanism for this purpose has entailed some dii'ficulties for the reason that the system pressure usually is very high, such as 3,000 lbs. p. s. i., whereas the .switch should remain open for all pressures higher than a much lower value, such as 75 lbs. p. s. i., and the switch should close to operate the signal for still lower pressure such as 40 lbs. p. s. vi., or less. One must guard against leakage into the switch mechanism, as oil would interfere with the proper operation of the switch. If the usual type of ring seal or other packing material in sufiicient amount is applied to a piston so as to effectively seal it against the system pressure of 3,000 lbs. p. s. i., the frictional load or hysteresis becomes so great that the piston is sluggish in its operation and the piston will not open or close at the desired low pressures within reasonably close limits.

Another problem arises in operating a switch, such as a micro-switch, in a positive manner, by the movement of a fluid pressure operated piston or the like, while preventing false operation due to the vibration of the aeroplane or the like in which the switch is mounted.

The present invention is an improvement of the hydraulic pressure operated switch described and claimed in application S. N. 286,991, filed May 9, 1952, for Hydraulic Pressure Operated Switch. In that application, the switch was actuated by a piston having spacing sealing grooves, a trigger being connected with the piston and part of the trigger being mounted on the casing which was of aluminum. As the device was subjected in actual use to a very wide temperature diiference, the difference in the expansion or contraction of the casing and the piston disturbed the adjustment of the trigger mechanism. Also the piston was lapped and ground, an expensive operation.

v Objects of the present invention are to reduce the cost of manufacture of the hydraulic operating mechanism for the switch and to prevent a wide temperature difference between the switch operating mechanism and the aluminum casing from disturbing the operation.

Another object of the invention is to facilitate substitution of one diaphragm for another one of diiferent strength so as to readily modify the device to operate at any one of several hydraulic pressures.

According to the invention, these objects are accomplished by providing a hydraulic switch operating mechanism in the form of a steel diaphragm and by providing an actuator therefor with a bracket to support the switch, independently of the casing. The diaphragm is provided with a backing plate to restrict its fiexure to the amount required to operate the switch while preventing flexure of the diaphragm beyond its elastic limit at the high pressures employed. The diaphragm construc-- tion is cheaper than the former piston and the expansion or contraction of the casing does not disturb the adjustment of the actuator for the switch. The diaphragm is unrestrained at its periphery and is removably mounted so that diaphragms of dilferent thicknesses may be substituted, one for the other, to provide for operation at any one of several high pressures.

By employing a lever having a mechanical advantage of less than unity, when high fluid pressure causes the diaphragm to actuate the switch, it is possible to employ a stiff diaphragm having a short throw for a switch plunger having a longer throw, whereas when the fluid pressure drops the lever has a mechanical advantage of greater than unity, so that the contact spring of the switch can operate the lever in moving the switch contacts to their alternate position.

For further details of the invention reference may be made to the drawings wherein Fig. l is sectional view of a hydraulic pressure operated switch according to the present invention.

Fig. 2 is a sectional view on the broken line 2-2 of Fig. 1.

Fig. 3 is a perspective view of the switch actuator, the full line showing the position of the lever for insertion through the casing nipple, the dotted line showing the operating position of the lever.

Fig. 4 is a perspective view of the switch, with parts broken away.

Referring in detail to the drawings, the hydraulic pressure operated switch ll comprises a casing 2 which may be of aluminum. Casing 2 has a bottom wall 3 from which arise side walls 4, 5, 6 and 7, defining a switch chamber 3. The casing 2. may be of other shapes. The casing 2 has a cover 9 having a ring seal 10, the cover being held in place by four screws like 11. The chamber 8 is airtight and it is evacuated through an opening 12 in wall 5 and then filled with an inert gas such as nitrogen, hole 12 being closed by a screw plug 13 having a ring seal 14.

Wall '7 has a hollow boss 15 having a cylindrical bore 16 in which sets the airtight base 1'7 of a socket 18 for the micro switch 20. Socket 1% .is held in place by screws like 19 and bore 16 is sealed by a sealing ring 21. Socket 1% is connected by wires 22, 23 to switch 20. Socket 1% receives the plug of a signal circuit, these items being well known and not illustrated, in order to indicate when the hydraulic pressure of the system to which pipe 24 is connected, reaches a certain low value.

Switch 20 has a plastic case 25 from which protrudes a pin operating plunger 26. Switch 2b is snap-acting and when plunger as is not operated, the circuit is completed through cantilever spring 27 connected to wire 22, and contact 23 connected to wire 23. The alternate contact 29 is not used, although it could be if desired. It is unnecessary to use it in the particular situation dealt with here for the reason that the requirement is that a signal be provided when the pressure drops below a certain value and hence it is only necessary to use the front contact 28. When plunger 26 is depressed, this operates spring 27 to open the circuit through spring 27 at contact 28 and spring contact 34. The bottom of the switch 29, as shown in Fig. 2, rests on a boss 30 arising from the bottom wall 3, while the top of switch 20 is urged against boss 30 by. a spring 31;. One end of spring $1 is housed in a recess 32 on the underside of cover 9, while its other end bears against bracket 35 on which switch 26 is mounted as indicated at 33.

Wall 7 has a hollow boss or extension 36 having internal threads 37 for a hollow nut or coupling 3%. Nut 33 has a lock nut 39 and has a threaded bore it? there for the pipe 24 which supplies oil under ln'gh pressure such as 3000 lbs. p. s. i. The extension 36, inwardly of threads 37 has a large bore 4?. which conjoins a small bore 42, the latter opening into the chamber 8. At the junction of the bores 41 and 42 is a shoulder 43 against which fits the side of a flange 44 at the outer end of a sleeve 45. The outer face of flange is concave as indicated at 46, and facing it is a flexible diaphragm 4'7 of steel or the The inner end portion 6% of nut 38 fits in bore ll. The inner face of nut 38 has an annular groove l) for an O- ring t} which makes sealing contact with the margin of the outer face of diaphragm 47. The periphery of flange 44 fits in bore 51, while the periphery of diaphragm #57 has a small clearance to permit it to flex under pressure. The concave backing face 46 restricts the fiexure of diaphragm 47.

When diaphragm i7 is flexed by fluid pressure in pipe 24, the inner face of diaphragm 47 abuts and pushes the outer end of a sliding pin 51 loosely supported in the axial bore 52 in sleeve or mount 4-5. Mount 45 inwardly of flange 44 has a cylindrical portion 53 which fits in bore 42, and the inner end of mount 45 has a disk portion 54 which also fits in bore 62. The mount 45 may be of steel and the disk 45 has an integral extension having longitudinally spaced bosses 56 and 57 having faces 53 and 59 lying in a plane and having threaded holes 66 and 61 for the screws 62 and 63, respectively which extend through longitudinal slots 64 and 65, respectively, in the bracket 35, to hold bracket 35 on extension 55. Laterally opposite boss 56 on extension 55 is boss 66 and a pivot or fulcrum pin 67 is secured in the spaced bosses 56 and 66. The bosses 56 and 66 define a slot '76 of uniform width in which swings the lever 68 on the pivot pin 67. Lever 68 is of uniform width slightly less than the width of slot 76 so that the bosses 56 and 66 guide and support the swinging movement of lever 68.

When the parts are assembled, pipe 24, nut 38 and diaphragm 47 being removed, the lever 68 is swung to a position shown in Fig. 3 extending lengthwise of extension 55 so that the lever 68 will embrace an area less than that of the bore 42 whereupon the mount 45 can be placed in position shown in Fig. 1 by inserting it into theh bores 41 and 42, with the extension 55 extending into the switch chamber 8.

After mount 45 is inserted in position, lever 68, which is longer than the diameter of bore 42, is moved to the position shown in Fig. 1 wherein it extends crosswise of the axis of bore 42, with the outer face 69 of lever 68 in abutting relation to the inner end 70 of pin 51, at a comparatively short distance from the fulcrum 67 and with the opposite face 71 of lever 68 in abutting relation with the switch plunger 26 at a greater distance from fulcrum 67.

As the mount 45 is fixed to the casing 2 only at its outer end by its flange 44-, and as the switch 20 and its driving connection with the diaphragm 47 are all carried by mount 45, the abutting relation of the various parts of this drive is not influenced by a different rate of expansion or contraction of the aluminum casing 2 and the steel mount 45.

Nut 38 is screwed in until the outer wall 77 of the O- ring groove clamps against the face of diaphragm 47. The inner wall 78 of the O-ring groove is shorter than the outer wall 77 and does not contact the diaphragm 47. The boss 36 has holes 79 and 80 to receive bolts or the like to hold the switch 1 on a suitable support not shown.

Loose play can be taken up to obtain an abutting relation between diaphragm 4-7 and the outer end of pin 51, between the inner end 70 of pin 51 and the face 69 of lever 68 and between the opposite face 71 of lever 68 and plunger 26, by loosening screws 62 and 63 and sliding bracket 35 lengthwise of extension 55. Bracket 35 has lengthwise slots 72 and 73 for screws 74 and 75 for threaded engagement with the switch casing 25. The lengthwise position of plunger 26 along lever 66 can be adjusted by loosening screws 74 and 75 to adjust the switch 20 along the slots 72 and 73.

When the normal high pressure exists on the outer face of diaphragm 47, this diaphragm is flexed a comparatively small amount, limited by the backing 46, to move the outer end of lever 68 a greater amount to depress switch plunger 26 to open the contacts 28 and 34. When the pressure acting on diaphragm 47 drops below normal, the diaphragm -37 assumes its normal planary shape and spring 27 acting through plunger 26 at a comparatively long lever arm, operates lever 68 and pin 51 to the position shown in Fig. 1, as an incident to closing the contacts 28 and 34. In other words, the loose mounting of pin 51 and the long lever arm through which plunger 26 acts, do not interfere with plunger 26 moving to its outer unoperated position when the fluid pressure drops below normal.

It will be apparent that various modifications may be made in the invention without departing from the spirit of the following claims. For example diaphragms of various thicknesses and materials may be used for diaphragm 47. Also, the switch shown in Fig. 4 is well known and forms no part of the present invent-ion, and other types of switches may be used instead.

I claim:

1. A hydraulic pressure operated switch comprising a casing having a bore, a mount removably fitting said bore, said mount having a slide bearing bore, a pin slidable in said bearing bore, a diaphragm in abutting relation to one end of said pin, a lever having one side in abutting relation to the other end of said pin, a fulcrum for said lever on said mount, a bracket on said mount, a switch casing on said bracket, said switch casing having contacts having a plunger in abutting relation to the other side of said lever, said bracket having slot means extending in a direction lengthwise of said pin and screw means therefor for adjusting said switch casing to adjust the abutting relation of said switch plunger, said lever, said pin and said diaphragm.

2. A hydraulic pressure operated switch according to claim 1, said bracket having slot means extending in a direction crosswise of said pin and screw means therefor for adjusting the position of said switch plunger lengthwise of said lever.

3. A hydraulic pressure operated switch according to claim 1, said casing having a switch chamber and a hollow extension having a cylindrical bore opening into said chamber, said mount having a cylindrical surface fitting said bore and said mount having an integral extension extending into said chamber, said fulcrum and said first mentioned screw means being mounted on said extension.

4. A hydraulic pressure operated switch comprising a casing having a switch chamber, said casing having a hollow extension having a bore opening into said chamber, said casing having a cover for said chamber, a sleeve fitting said bore, a hydraulic diaphragm, means for supplying fluid pressure to one side of said diaphragm, said sleeve having an extension in said switch chamber, a lever having a fulcrum on said extension, said sleeve having a slide bearing bore having a sliding pin in abutting relation to the other side of said diaphragm and one side of said lever, said lever having a length greater than the diameter of said bore, said extension having a removable bracket having a switch having a plunger for the other side of said lever, screw means for removably securing said bracket to said extension, means removably securing said switch to said bracket with said lever extending crosswise of and beyond said smaller bore, said lever being movable on its said fulcrum to occupy an area less than the area of said bore, when said bracket and said switch are removed, for insertion of said extension and said lever into said switch chamber through said bore.

5. A hydraulic pressure operated switch comprising a casing having a switch chamber, said casing having a hollow extension having a larger bore at its outer end and communicating with a smaller bore opening into said chamber, said casing having a cover for said chamber, a sleeve having a concave outer end of a size fitting said outer bore and a portion of reduced size fitting said smaller bore, a hydraulic diaphragm in said larger bore in face to face relation to the outer end of said sleeve, a fitting in said outer bore having a fluid passage therethrough and having a ring seal for the outer face of said diaphragm, said sleeve having an extension in said switch chamber, a lever having a fulcrum on said extension, said sleeve having a slide bearing bore having a sliding pin in abutting relation to one side of said diaphragm and one side of said lever, said lever having a length greater than the diameter of said smaller bore, said extension having a removable bracket having a switch having a plunger for the other side of said lever, screw means for removably securing said bracket to said extension, means removably securing said switch to said bracket with said lever extending crosswise of and beyond said smaller bore, said lever being movable on its said fulcrum to occupy an area less than the area of said smaller bore, when said bracket and said switch are removed, for insertion of said extension and said lever into said switch chamber through said smaller bore.

6. A hydraulic pressure operated switch comprising a casing having a switch chamber, said casing having a Wall having a bore opening into said chamber, a mount, said mount having a portion fitting said bore and having another portion freely extending into said chamber, said bore having a diaphragm, means for admitting fluid pressure to said diaphragm, a switch casing on said mount in said chamber, said switch casing having contacts having a plunger oif center from said diaphragm, and a drive connection between said diaphragm and said switch plunger carried by said mount and means for fixing the outer end only of said mount to said casing, the remainder of said mount being free of attachment to said casing whereby the operative relation of said drive to said diapragm and said switch plunger is not influenced by expansion or contraction of said casing at different temper atures.

7. A hydraulic pressure operated switch comprising a lever having a fulcrum, a plunger, means supporting said plunger in abutting relation to one side of said lever at a certain distance from said fulcrum, fluid pressure operated means for actuating said plunger, said plunger supporting means having an extension, said extension supporting said fulcrum, a switch having a spring-operated plunger and means supporting said switch on said extension with its said spring-operated plunger in abutting relation to the other side of said lever at a greater distance from said fulcrum than said first mentioned plunger.

References Cited in the file of this patent UNITED STATES PATENTS 708,155 Meloon Sept. 2, 1902 1,951,245 Jardine Mar. 13, 1934 2,404,843 Huber July 30, 1946 2,428,096 Reavis Sept. 30, 1947 2,435,143 Knauth Jan. 27, 1948 2,492,261 Bordelon Dec. 27, 1949 2,562,385 Marcellus July 31, 1951 

